1. Field of the Invention
The present invention pertains to blowout preventer control apparatus. Specifically, the present invention pertains to control apparatus suitable for preventing inadvertent operation of the drawworks of the drilling rig upon closure of an associated blowout preventer, the drawworks being at least partially operated by air.
2. Brief Description of the Prior Art
Since the early days of the petroleum industry, "blowout" of a well during drilling operations has been a major concern. If the proper precautions are not taken, the drill bit may enter a high pressure formation forcing oil and/or gas to rush out of the well creating hazards to both life and property. Since the late nineteenth century, various types of flow control devices have been developed to prevent such blowouts. These flow control devices, known in the industry as blowout preventers, may be classified under one of three broad types: the inverted packer type; the ram type; and the stuffing box or pressure operated drilling packer type. The purpose of any of these types of blowout preventers is to seal the annular space between the drill stem and the casing quickly, easily and safely.
One of the most popular and widely used of these three types of blowout preventers is the ram type. Such preventers generally comprise a housing which may be attached to the well casing and which is provided with a passageway through which the drill pipe may be passed. Carried in the housing is a pair of rams which are disposed for reciprocal movement between a retracted or open position, in which the annular area between the drill string and the blowout preventer passageway is open, and an extended or closed position, in which the rams engage the exterior of the drill string and sealingly close the annular space between the drill string and casing. The rams are usually connected by a rod to a piston and cylinder assembly carried by the blowout preventer housing. To close the blowout preventer, hydraulic pressure is applied to the piston and cylinder assembly, forcing the rams into sealing engagement with the drill string. To open the blowout preventers, pressure is simply applied to the opposite end of the piston and cylinder assembly. Such pressures are normally provided by manual manipulation of a hydraulic control mechanism.
Drilling rigs are also provided with drawworks which among other things is used to raise and lower the drill string. Most modern day drawworks are provided with an air operated clutch assembly to which air is supplied by an air source, commonly referred to as "rig air".
If the ram-type blowout preventer has been closed and the drawworks are inadvertently engaged to lift the drill string, damage may occur to the rig or the drill string. In fact, it may cause the drill string to be severed, dropping thousands of feet of drill string in the well hole. This may require an extremely costly "fishing" operation and in some cases even require that the hole be abandoned. Recognizing the extreme cost of the present day drilling for oil and/or gas, it is easily seen that such inadvertent operation of the drawworks should be prevented if at all possible.